NEUROPROTECTIVE EFFECT OF THYMOQUINONE AGAINST GLUTAMATE-INDUCED TOXICITY IN SH-SY5Y CELLS

摘要

Thymoquinone (TQ), the most abundant bioactive constituent of the essential oil of Nigella sativa Linn. seeds, has shown diverse therapeutic effects. The present study investigated the protective mechanisms of TQ against glutamate-induced cell death in SH-SY5Y neuronal cells. To assess the protective effect of TQ on neurons, SH-SY5Y cells were pretreated with TQ (0.1-3 mu M) for 18 h, followed by treatment with glutamate (8 mM) for additional 8 h. Cell viability was measured by 3-(4,5-dimethylthiazol-2-yl)-5(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium inner salt assay. Glutamate-induced reactive oxygen species (ROS) generation, mitochondrial dysfunction, and markers of intrinsic apoptotic pathway were also tested by Western blotting. Exposure of cells to glutamate caused viability loss, ROS generation, mitochondrial dysfunction and increased the apoptotic cascade by increasing the Bax expression, decreasing Bcl-2 expression and caspase-9 activation. TQ cotreatment, however, dose-dependently increased cell viability and attenuated ROS generation. Rhodamine-123 assay revealed that glutamate markedly increased the mitochondrial membrane potential, and this increase was dose-dependently attenuated by TQ cotreatment. Western blotting indicated that TQ cotreatment markedly increased bcl-2 and had no effect on Bax expression, thus decreased Bax/Bcl-2 ratio as well as caspase-9 expression compared to glutamate treatment alone. These results suggest that TQ effectively protects against glutamate-induced SH-SY5Y neuronal cell death and inhibits ROS generation, mitochondrial dysfunction and intrinsic apoptotic cascade.